1. Technical Field
The present invention relates generally to the field of computer cooling, and more particularly to an apparatus and method for enhancing the cooling of dual in-line memory modules.
2. Description of the Related Art
Dual in-line memory modules (DIMMs) are a dominant form of packaging dynamic random access memory (DRAM) modules in computer server applications. Multiple DIMMs are normally placed in parallel, on a narrow pitch (9 to 12 mm), and in close proximity to high-powered CPU processors. Multiple DIMMs may be configured in a variety of capacities and form factors, creating a mixture of differing airflow geometries in the same system. A system with a 12 DIMM capacity may be populated with 12 DIMMs. However, a system with 12 slots may include only 4 DIMMs and 8 vacant slots. As another example, a system with 12 slots may include eight single-high and four double-high DIMM form factors.
Vacant slots and/or mixtures of DIMM card heights present regions of relatively low air flow impedance in parallel with much more restrictive flow channels. The effect of this imbalance, since air takes the path of least resistance, is flow starvation in regions of higher DRAM density. This flow starvation may result in component overheating, reduced reliability, and loss of function.
Existing solutions include increasing fan/blower flow delivery and obstructing the open channels with foam blocks or other filler designs. The drawbacks of increasing fan output to offset the flow bypass imbalance include increased acoustic noise level, increased electrical power consumption, increased air moving device size and cost, and increased bearing temperatures. The drawbacks of complete obstruction of open channels with foam blocks or the like include increased overall system pressure drop, which results in the same disadvantages as listed above for increasing fan output, and increased heating of downstream or upstream components, as the mass flow rate is reduced as a result of increased pressure drop. Typically, the flow through the DIMM bank area is passed serially through a high-power CPU region and therefore cannot be overly restrictive.
Existing DIMM fillers provide some degree of flow balancing; however, they do not handle combinations of multiple height DIMMs, and they lack any means of focusing the flow over a hub chip. In order to provide the same amount of cooling to a hub chip, prior art fillers require much higher airflow rates. On-DIMM hub chips are a relatively recent addition to memory DIMMs, having been added to increase memory speed and capacity as processor architectures increasingly improve bandwidth access to memory. Overheating of memory DIMMs is currently a problem for DDR2 DIMMs and is expected to get worse for the next generations of DIMMs (DDR3 and DDR4) because DRAM device powers and CPU preheat are increasing, while the industry allowable temperature limit for single-refresh DRAMs remains fixed at 85° C.